This invention relates to monitoring systems that use electro-optical transmission lines to transmit sensor data to a central processor.
Electro-optical transmission systems are known in which electrical signals are coupled to a first electrical connector member where the signal is converted by means of a light-emitting diode (an "L.E.D.") to an electrical output signal, and the output signal is transmitted by a fiber-optic cable to a light-receiving diode in a second connector member which receives the optical signal and converts it back to an electrical signal. Such electro-optical transmission systems have the advantage over conventional hard-wire transmission systems in that they are not susceptible to electro-magnetic interference ("E.M.I.") and radio frequency interference ("R.F.I."). Since these systems are not subject to electrical noise, they are often used in high technology situations, such as monitoring systems in satellites, to precisely transmit electrical data.
Besides being relatively immune to electrical noise, another aspect which makes the fiber-optic cable attractive is the lighter weight of the cable as compared to a shielded link using conventional hard wire. Further, fiber-optic links also have a greater bandwidth, which enables more information to be transmitted if the information is multiplexed.
While these systems have proved quite useful, especially in satellites for transmitting information from a remote sensor with a high degree of accuracy, these systems have a serious drawback. Their L.E.D.s are usually kept "on" even when information is not desired. Thus, the L.E.D. of most prior systems quickly burns out. And, as soon as it does, the system is useless. The system can no longer transmit information until the L.E.D. is replaced.
While this may be only a minor setback in places where the diode can be easily replaced, it is fatal when the system is in a remote area, where repair is unfeasible. Consequently, a need exists for a system in which the life of the L.E.D. is prolonged.